Neuropeptide Y mediates orexin A-mediated suppression of pulsatile gonadotropin-releasing hormone secretion in ovariectomized rats

Objectives : Reproductive functions are influenced by various feeding regulators.
Orexin, which is one of orexinergic peptides, suppresses the pulsatile secretion of
luteinizing hormone (LH) in bilaterally ovariectomized (OVX) rats. However, the mechanism
of this effect is still not clear. To investigate whether neuropeptide Y (NPY) is involved
in the orexin A-mediated suppression of pulsatile LH secretion, we evaluated the
effects of NPY antibody on the suppressive effect of orexin A. Methods : Orexin A was administered
intracerebroventricularly (icv) and NPY antibody (NPY-Ab) was injected before
icv administration of orexin A in OVX rats. Pulsatile LH secretion was analyzed by
measuring serum LH concentrations in the next 2 h in blood samples drawn at 6-min intervals
by radioimmunoassay. Results : Administration of orexin A significantly reduced
the mean LH concentration and LH pulse frequency. Co-administration of NPY antibody
with orexin A significantly restored the suppressive effect of orexin A on the mean LH
concentration and LH pulse frequency. Conclusion : NPY mediated the suppressive effect
of intracerebroventricularly injected orexin A on pulsatile LH secretion, suggesting that
hypothalamic orexin suppressed pulsatile gonadotropin-releasing hormone (GnRH) secretion
via NPY in the hypothalamus of female rats.

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